The invention relates to a surgical device for fixing bone elements, having an elongated, flexible clamping means for winding round and bracing the bone elements to be fixed, having a connecting part for connecting the ends of the tightened clamping means, a first end of the clamping means being fastenable to the connecting part and the second, free end of the clamping means being passable through an opening of the connecting part so as to form a loop, and having a locking member supported counter to the clamping direction against the connecting part and non-releasably connectable to the clamping means.
Such devices are used, in particular when setting oblique fractures of long bones, in the form of so-called cerclages where a clamping means, e.g. a wire loop or a metal strip, is wound round the bone elements to be fixed and then tensioned by means of a tensioning tool. The cerclages comprise a connecting part in the form of a cerclage clasp, by means of which the ends of the tensioned clamping means may be connected to one another. The cerclages are usually pre-fabricated by fastening a first end of the clamping means to the connecting part. The second, free end of the clamping means may be passed around the bone elements to be fixed, so as to form a loop, and then through an opening of the connecting part. The free end is then fixed to the connecting part.
The cerclages may be combined with additional osteosynthesis or internal fixation implants. Said option is used, for example, in surgery to the dorsal vertebral column. In the region of the thoracic and lumbar vertebrae, cerclages are used in conjunction with rod-shaped longitudinal supports for segmental correction and stabilization. To said end, the clamping means may be passed under the vertebral arches (sublaminar passage). Such methods are used, for example, for scoliosis, kyphosis, tumours and fractures. In the region of the cervical vertebrae, adjacent vertebral arches are connected by cerclages, e.g. in cases of fractures as well as post-traumatic and rheumatic instability. In many cases, sublaminar cerclages are also used in combination with screws and hook assemblies since, because the pedicle size in the thoracic vertebrae region decreases towards the head, a transpedicular screw fixation is no longer possible.
A basic requirement of such devices for fixing bone elements is that they should enable as simple as possible an operating technique, i.e. they should be easy to handle. A further important point is that over an extended period of time they should reliably exert a high clamping force upon the bone elements to be fixed. Since a plurality of cerclages are often used simultaneously, they should be designed in such a way as to allow first a temporary fixation during an operation so that a subsequent increase of the tension of the cerclages and a correction of the mutual position of the bone elements is possible.
To facilitate a subsequent increase of the tension of the cerclages, devices have already been proposed which operate on the principle of a cable binder (U.S. Pat. No. 4,667,662, WO 94/26192 as well as DE 27 30 571 C2) or a hose clip (DE 40 21 246 A1, DE 42 00 757 A1, DE 34 27 590 C2, DE 32 44 680 A1). In such systems, the clamping means comprises a tooth system, into which a corresponding pawl engages so that the cerclage is secured by means of a form-fit locking mechanism. The tooth system, however, poses a not inconsiderable risk of injury to the body tissue surrounding the bone elements to be fixed. Furthermore, although such refinements do guarantee a subsequent increase of the tension of the clamping element, a permanent fixation of the clamping means is not always guaranteed. Instead there is a danger of the clamping means loosening as time passes.
Cerclages are also known which use pressure clamps to fix the clamping means, a plurality of pressure clamps being threadable onto the clamping means. If, after tightening, the pressure clamp adjacent to the tensioning tool is first compressed, then after a readjustment of the tension the next pressing clamp inwards may be secured.
Such systems entail a relatively complex operating technique and the pressure clamps are easy to lose and difficult to manipulate.
Pressure clamps are also known which are permanently connected to the connecting part (WO 95/06438, U.S. Pat. No. 5,395,374, WO 95/03002). A temporary fixing is not possible with such refinements. To said end, additional clamps which are mountable onto the connecting part are provided, thereby making the operating technique not inconsiderably harder. The additional clamps moreover take up a substantial amount of room.